The present invention relates to a override device for malfunction in fuel injection systems, intended in particular for compression ignition engines such as diesels.
Persons familiar with the design of diesel engines know that a typical fuel injection system comprises two basic components by means of which fuel is supplied to the combustion chamber, namely, the injection pump and the injector.
Of fuel injection systems currently in use, the most widely adopted is the mechanical type, which offers uncomplicated design and operation, together with notable dependability, and is both simple and economical to maintain.
Numerous types of equipment have been developed for mechanical fuel injection; these fall into two main categories: those utilizing a common rail, which simply accumulate pressure, and those using a timed jerk pump to generate pressure intermittently.
The following specification refers exclusively to the second, timed type of system, currently in the ascendancy due to its adoption in high/medium speed diesel units of which the development has ballooned in recent times; whichever pressurization is used, at all events, two methods of fuel injection are possible: indirect, whereby fuel is injected into a combustion chamber remote from the piston, and direct, where the combustion chamber is formed in the crown of the piston itself.
The recent development in question stems largely from the notion of using diesel engines to propel light airplanes suitable for tourism; naturally, the key requirements for such engines will be connected with safe and dependable operation.
The fuel injection system in compression-ignition engines consists in a plurality of pump elements, corresponding in number to the cylinders of the engine, which supply the fuel through short pipes to a similar number of injectors.
The various elements of the injection pump, each supplying a relative injector, are mounted in a single crankcase disposed generally parallel with one another and operated by a camshaft rotating synchronously with the engine, with which contact is made through roller tappets. The volume of fuel delivered by each pumping element per unit of power required is metered through a measured rotation of the plunger of the pumping element itself, effected conventionally by means of either rack-and-pinion or rod-and-crank type linkages.
Precisely because of its structural configuration, this linkage can give rise to drawbacks of a nature such as seriously affect the normal running of the engine, one of which deriving from the rigidity of the rack or rod. In effect, should even one only of the pumping elements become jammed, due in most instances to the plunger seizing in the relative bore, this will inhibit control over the remaining elements as all are mechanically interlocked.
Whilst a malfunction of this kind could perhaps be regarded as little more than inconvenient in the engine of a vehicle or other power transmission on land, it is certainly unacceptable and hazardous in an aero engine; rather, in the interests of safety in flight, a loss of control over just one pumping element of the fuel injection system must in no way affect normal control over the remainder.
Accordingly, the object of the present invention is to overcome the drawbacks described above through the adoption of a control rod provided with one or more devices, installed in number equivalent to the number of elements of the injection pump, that will be capable of by-passing a possible malfunction of the nature outlined above and therefore of enabling the remainder of the fuel injection system, hence the engine, to continue operating substantially as normal.